Process of chemical nickel plating and bath therefor



Nov. 10, 1953 GUTZEIT ETAL PROCESS OF CHEMICAL NICKEL PLATING AND BATHTHEREFOR Filed Nov. 8, 1.950

7 Sheets-Sheet 1 Temperature C FIG I u &9 E E: k N $2 3 55 5 .5%

m v, 0.0 e

fb G A Nov. 10, 1953 e. GUTZEIT EAL 2,658,841

PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR Filed Nov. 8, 19507 Sheets-Sheet 4 E a 26 (H P0 0.224 MO/E/LIIGI' g (0 11 02): 0. I20Mole/Lifer E Inifial pH= 5.5 5 Q 22 Na J u m s g g 0 v/A=I0.0 g g t:18-- i 6 E l I I I l l l l g g 012 014 0.6 010 1.0 /'.2 1.4 8 Ratio,Nickel Ions Hypophosphife Ions.

FIG. 6

g 54-- Q g} 52-- (H3PO2)= 0.224 Mole/Lifer 50- (Cg/I302 r= 0.120Mole/Lifer Q) g Initial pH 5.5

Q on E uva 1 1; 44-- u L '5 g 42 32 I 40 E g 5 38+ V/A 20.0 0. 5 w g 36-E, 0 1 ois 055 017 0.9 /f/ 1'3 3 Ratio, Nickel Ions Hypophosphifefons.INVENTORS FIG 7 Gregoire Gufzeif BY Abraham Krie Nov. 10, 1953 G.GUTZEIT ETAL PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR 7Sheets-Sheet 5 Filed NOV. 8, 1950 4 r r I. 8 6 h H S L L n 2%. w m 0 0 MM m 0 :om Q h 8 0. 0 w- 6 H I 2 D. 2 0 F 0 0 H N 2 M m M .E II. I OH k w.N 0 m m :2 0

0 0 0 0 0 m 8 6 4 2 5335 B SE Q$ m BEE M 2 2 l I EQ\QE =5: 2 5 53 3 5 Bim Ex s EEQ 39$:

FIG. 9

Abraham Krieg Affys.

Nov. 10, 1953 Filed Nov. 8, 0

Weight of Plating (Nickel 8 Nickel Phosphorus) Weight of Plating (Nickel8 Nickel Phosphorus) Deposited in One Hour mg /cm Deposited in One Hourmg/cm G. GUTZEIT ETAL 2,658,841

PROCESS OF CHEMICAL NICKEL PLATING AND BATH THEREFOR 7 Sheets-Sheet 6(cw/302) o./2o Mole/Liter (H P0 0.224 Mole /Liler 0.2 014 0. 6 o e i0/.'2 [4 Ratio, Nickel Ions Hypophosphite Ions. F I 6.. IO

(HgPOgF 0.224 Mole Liter (0 H 0 0. I20 Mole Liter ICa J pH 4.7 W pH 5.02/

0 .2 0E4 0. 6 0E8 l .0 .2 If4 Ratio, Nickel Ions Hypophosphite Ions.

' ,INVENTORS [3 I Gregoire Gutzeit Abraham Krieg A ti ys.

Patented Nov. 10, 1953 PROCESS, OF CHEMICAL NICKEL PLATING AND LBATHTHEREFOR Gregoire Gutzeit, Highland, and Abraham Krieg, Gary, Ind.,assignors to General American Transportation Corporation,0hicago,- Ill.,a.cr- .poration of New York Anplicationz Novemben 8, 1950, Serial"N051943656 12 Claims. (01.117-130) The present invent-ion: relates toprocesses -.of chemical nickel plating and -.to vbaths employed incarrying out such processes.

The purpose of the inventionis to provide a chemical plating :process.which will have :many advantages in commercial use over electroplatingmethods, including low cost of equipment, good adhesion of .the coatingin the finished product, high corrosion resistance of .the coating, anda coating which is uniform, continuous and much harder.

Eiforts have heretofore: beenmade -.to obtain some of thesedesirable-results-by:coating processes but without su-fiicient success.to warrant the commercial use of the methods suggested. For example, ithas been ::proposed' by Brenner and Riddell (Jour. Research,vNationalsBureau of Standards; vol. 37, -July. 1946, and vol. v3 9,;November, 1 947)thatcoatings ofnickel=may:be deposited upon --thesurfaces of catalytic -metals, for example, mild .steekeby employingachemical reduction of nickelions froman-aqueousbath containinghypophosphiteions in thepresence of sodium: ions and. sulfate ions.andusing-sodium acetate as a buffer .tomaintain-the pH-of-the bath inthe range ofiromal to 6,-the temperature of the .bath being maintainedat about 190 -icen tigrade. For instance-,iBrenner and .Riddell: suggesta numberotbathse one of: which comprises nickel sulfate gms/liter)sodium: hypophosphite (10 .gms/Iiter), and sodium acetate (10gms./liter). In all:of :.these .baths,- the ratio of nickel ions tohypophosphiteiions Ni l'fi-HPoz)" expressed in terms,-.-of molarconcentrations was a. decimal fraction, sis approximately 1133 and theabsoluteconcentrationof hypophosphite'ions is approximately 0.095.mole/liter. Employing this bath Brenner, and :Riiddell .obtained thedeposition of the nickel-uponathe surface of the; steel at a rate of0.015zmillimeter per hour.

In such a chemical: plating process, thez-principal reaction,.in thepresence of water, expressed in ionic .form is considered to the: i

the nickelionl and sodiumxhypophosphitezto providethe" hypophosphiteion:

certain advantages over "competitive electrolytic processes, it wasz-found by them to :be-uneconomical, to produce deposits at -.a slowrate .and to lack control of the composition of the :deposits. It isconsiderably more expensive to carry out thanthe-competing:electrolyticprocesses due primarily to'the low nickelefliciency ofwthe reaction, i. e.,' therper cent of nickel actuallydeposited at completion, as related-to the total amount of nickelpresent in'the :bath initially.

Accordingly, it is a general object of the present invention toprovidean improved chemical nickel plating iprocess of the general characterdescribed, in which therreaction involved; is=.carried out in anefiicient manner which renders the process economical from a commercial;and industrial standpoint.

Another object: of :the' inventionxis to provide antimproved.aqueoustibath-lof thezgeneral character' described .that. may beemployed with: ad vantage in carrying. .out. :the improved 2. process.

A further object of the invention is to provide an improved process ofchemical nickel plating and an improved aqueous. bath thatsmay. beemployed. in carrying: out thexprocess, whereby the surfaces ofcatalytic materials. may he. readily coated with nickel in asimpleandefficient manner and wherein .the nickel coatings ..are smoothand continuous andtare' of alowporosity and of high corrosion resistanceand are intimately bonded tothe surf'aceof'the catalytic material.

A further object of: the 'invention is to provide an improved process ofchemical nickel plating and an improved aqueous bath that may beemployed in carrying out the processthatare adapted for the commercialcoating of iron, steel and the like.

Further featuresof the-invention pertainto the particularl arrangementof the steps of: the processand to'the compositionofthe aqueous bath,whereby the above mentioned objectsof the invention andothersareattained.

The invention, both as to its organization and principle of operation,together with further objects and I advantages thereof,--will best beunderstood by-referenceto the following 'specificatioh taken -inconnection with th'e accompanying drawings in which, i

Figure 1 shows the relative amounts of plating deposited-with changes-intemperature;

Fig. 2- shows the variationof the weight *of 1 plating depositedinsagiven period with variation nickel ions .-tohypophosphite ions of theratio of nickel ions tohypophosphit ions; Fig.3 shows the change .inthe.pH value after a given period with :vari'ation of the. ratio .iof

Fig. 4 shows the variation in the weight of the Fig. 6 shows thevariation of the weight of the plating deposited with variation in theratio of nickel ions to hypophosphite ions when using a higher ratio ofbath volume to plating surface area than that employed in the testsrecorded by the curves of Fig.

Fig. 7 shows the variation of the weight of the plating deposited withvariation in the ratio of nickel ions to hypophosphite ions derived fromsodium hypophosphite Fig. 8 shows the variation in nickel efiiciency, inper cent at completion, with variation in the ratio of nickel ions tohypophosphite ions;

Fig. 9 shows a series of curves illustrating the variation in the weightof the plating deposit with variation in the pH of the plating bath fordifferent specified ratios of nickel ions to hypophosphite ions derivedfrom sodium hypophosphite;

Fig. 10 shows the variation in weight of the plating deposit withvariation in the ratio of nickel ions to hypophosphite ions derived fromsodium hypophosphite for two specified pH values for the bath;

Figs. 11 and 12 show a series of curves illustrating the variation inthe weight of the plating deposit with variation in the pH of theplating bath for different ratios of nickel ions to hypophosphite ionsderived from calcium hypophosphite; and

Fig. 13 shows the variation of the weight of the nickel plating depositwith variation in the ratio of nickel ions to hypophosphite ions derivedfrom calcium hypophosphite with the use of calcium acetate as a butter.

In accordance with the process of the present invention, the catalyticmaterial that may be coated with nickel comprises any material in thesolid phase which will initiate at its surface the reaction of Equations1 and 2 set forth above; i. e., a material which, when immersed in thebath, will cause the evolution of hydrogen gas at its own surface.amples of catalytic materialswhich may be nickel plated: copper, silver,gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon,vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium,iron, cobalt, nickel, palladium and platinum; and the following elementsare examples of noncatalytic materials which ordinarily may not benickel plated: bismuth, cadmium, tin, lead and manganese. The

gassed nickel (containing some phosphorus).

The following elements are exthe nickel ions.

activity of these catalytic materials varies considerably. The followingelements are particularly good catalysts in the chemical nickel platingbath hereinaiter set forth, viz: aluminum, carbon, chromium, cobalt,iron, nickel and palladium.

" Thus, the nickel plating process becomes autocatalytic, when both theoriginal surface and the met-a1 that is deposited are catalytic, and thereduction of the nickel salt to metallic nickel in the bath inaccordance with the reaction of Equation 2 proceeds until all of thenickel ions have been reduced to metallic nickel, in the presence of anexcess of hypophosphite ions, or until 4 all of the hypophosphite ionshave been oxidized to phosphite, in the presence of an excess of nickelions. Actually the reaction of Equations 1 and 2 is slowed down ratherrapidly as time elapses, because the anions, as contrasted with thecations, of the nickel salt combine with the hydrogen cations to form anacid, which, in turn, lowers the pH of the bath tending to dissolve thenickel deposit. This reaction is considered to be:

Also, the reducing power of the hypophosphite ion is decreased as the pHvalue decreases. It is, therefore, important to prevent a rapid drop ofthe pH of the bath after initial adjustment thereof within its optimumrange. This-can be achieved by various schemes both alone and incombination. For example, a soluble nickel salt of a weak acid, such asacetic acid, can be used both to provide nickel ions and to act as abuffer. Also, the pH of the bath can be corrected periodically by theaddition of a weak alkali, such as sodium bicarbonate; or a buffer, suchas sodium acetate or other alkali acetate, can be added to the bath.

In carrying out the process, the article to be plated and normallyformed of the catalytic material is properly prepared by mechanicallycleaning, degreasing and light pickling, according to the standardpractice in electroplating processes. For example, in the nickel platingof a steel object, it is customary mechanically to clean the rust andmill scale from the object, to degrease the object, and then lightly topickle the object in a suitable acid, such as HCl. The article is thenimmersed in a suitable volume of the aqueous bath containing the properproportions of nickel ions, hypophosphite ions and a buffer, the pH ofthe bath having been first adjusted to an optimum value by the additionof a suitable acid, and the bath having been heated to a temperaturejust below its boiling point, such as 99 C. at atmospheric pressure.Almost immediately, hydrogen bubbles can be observed forming on thecatalytic surface of the steel object and escaping in a steady streamfrom the bath, while the surface of the steel object is slowly coatedwith The reaction is continued until the color of the bath (green at thestart) shows the absence of nickel, or until the evolution of hydrogengas stops.

A nickel plating bath, as indicated above, containing a soluble nickelsalt, a soluble hypophosphite and a bufier, is only relatively stable;and even without the presence therein of a catalytic surface, it tendsto decompose more or less rapidly by random chemical reduction ofSpecifically, the nickel ions are reduced as a fine amorphous, blackpowder, which, in turn, acts as a catalyst. The resulting precipitate isgray to black and contains various quantities of nickel, phosphorus andsalts, depending on the conditions of formation. This spontaneousdecomposition is a function of temperature, time and initial bathcomposisition; and insofar as the initial bath composition is concerned,the higher the ratio of hypophosphite ions to nickel ions and the higherthe absolute concentration of hypophosphite ions, the more unstable isthe bath. In other words, instead of a bath capable of controlled nickeldeposition in the presence of a catalyst,

a high concentration of hypophosphite anions will produce the well-knownpurely chemical nonselective reduction of nickel ions. Under platingconditions, in the presence of a catalytic g ef and at an elevatedtemperature, thecontrolledchemical reduction of the nickel ions in thebath, thus depleting the bath. Also, the

presence of the black precipitate in the bath results in a dull, roughand uneven nickel coating upon the object that is undergoing the plat--ingreactioni I v "In carrying=out the process, the-rateof catalyticreductionof nickel'ions tometallic nickel is-a function of temperatureof the bath and.-

this function logarithmic; forexample, if the temperature ofthe bath isdecreased from approximately 100 C; to-approximately 90 0., ithas beendiscovered that the plating rate drops approximately "52.5%. It is,therefore, important that thetemperature of the bath be maintainedatthehighest possible temperature below the boiling point thereof underthe prevailing conditions, which is under standard conditions a.

temperature of approximately 99C.. Tests have been made to determinethe. weight of nickel deposited per hour by the method of the presentinventionsat different temperaturesand the results between 930? and 100?C. have been plottedto form the curve l8 shownin Fig. 1 of the drawings.

While it is apparent that there is a definite relationship involving theplating, rate of the object in thebath between the volume of the bath.andv the, surface, area of the object, ithas been. -discovered.,.thatthe volume of. the bath also determines the: relative amount. of blackprecipitate that'is formed under otherwise similar conditions. Thus,as'the volume increases, the amount. of. black precipitate increases.Employing the notation: V/Af for the ratio b. tween the volume of the.bath expressed in cubic centimeters (cm3) and. the geometric surfacebeen. found that certain alkaline cations that are thus introduced intothe bath appear to retard the rate of nickelv deposition with respect toother cations. For example, barium ions ape pear to retard the rateof;nickel deposition with respectfto sodium; and potassium ions; Omtheother hand, certain cations that are thus introduced into the bathappear to accelerate the rate of nickel deposition with; respect toother cations.- Eor example, masn s u1n ns; app a to accelerate therate:of nickel: deposition with respect to. sodium. and potassium ions.Ac.- cordingly, from afstandpoint of economy, sodium and. calciumhypophosphites: are recommended; and from a standpoint of: realizing thema-ximumw rate of nickelv deposition, magnesiumhy:

pophosphiteis-recommended. a

' decomposition, is

In preparing the bath, the amounts or sol uble nickel salt and: solublehypophosphite'that areemployed are such that both the ratio of nickelions to hypophosphite ions and the abso I lute concentration ofhypophosphite ions are initially established within optimum ranges.

The term ion'as employed herein includes thev total quantity of elementor radical present in.-

the bath; i. e., both undissociated and dissociated material. In otherwords, dissociation is assumed when-the; term ionis used in connectionwith molar ratios and concentra.-. tions in the bath. The ratio betweenthe nickel ions and the hypophosphite'ions, Ni++/(H2PO2)'-:,

; in terms of molar concentration may be ex- 'pressed as a decimalf'raction; and it has been discovered that the most favorable rangeofthis fraction lies between 0.25 and 0.60. It has also been discoveredthat the required absolute concentration of the buffer anions, such asacetate ions, should be equivalent to two carboxyl groups per ion ofnickel that can be reduced, as explained morefully hereinafter. Forexample, if a hypophosphite ion concentration of .225; mole/liter ischosen, the required absolute concentration of acetate ionsof thebuflfer; ex-

pressed in mole/liter, would be apPrQXimately- The relationshipbetweenthe ratio,

This curve has been plotted phosphite ions was 0.035 mole/liter, as the-Brenner and Riddell baths derivedfrom'sodium hypophosphite, the absoluteconcentration of acetate ions was-0.120 mo1e/1iter, the. V/A-ratiowas/5; the temperature of the bath was approximately 9e 0., and"thinitial-pHof the bath was in the range of'frorn' 5.38 to 5.49. InFig. 2- the abscissae show the ratio of nickel ionsto hypophosphitetionsand the ordinates show the weight of the plating-deposited in-a periodof'two' hours in milligrams-persquare centimeter. It will be observedthat the highest 'plating rates were obtained when the ratio ofnickelion s to hypophosphite tt 7 I In the zone where the -higest platingrate-Was -obtained, the coating -was als'o cf thebestquality. beingbright andasmooth. The lower plating rates were characterized by a dulland rough coating: The zone where the coating was bright and smooth hasbeen indicated in Fig. 2 b-y-the-nota tion be. and the zone where-thecoating-was-dull and rough hasbeenind -icated by the notationdr.

In the event the .absol-uteconcentration of hypophosphiteions-in thebath is increased while maintaining constant the nickel ions tohypophosphite ions ratio, an increased ratecf nickel deposition isrealized, until a region-is reached where the bath becomes unstable suchthat-spontaneous decomposition thereoftakes place with the resultingformation of theblack precipitate previously referred-to.

It has been discovered thatthe optimum absolute concentrationofghypophpsph-ite i'ons in the bath, 1, e., onethat will result ingood-nickel-plating without an excessive ten rlency to spontaneouswithin-the range-0.15 mole/liter. to 0.35 mole/liter; and .approximately-0.22 5 mole/liter is recommended. Moreoverf'thespo sta'ntiabsoluteconcentration of hypophosphite with the results of V a test in which theobject plated was formed of mild steel, the absolute concentration o fhypoio s sin the ran 5t 1-6Q-.,

ions is related to the ratio, Ni++/(l-Izl Oz)-, as

illustrated by the curve 22 shown in Fig. 3 which shows, with varyingratios of nickel ions to hypophosphite ions, the drop in pH value afterthree hours at 99 C. without a catalyst.

In these tests, represented by the curve 22 of Fig. 3, the absoluteconcentration of hypophosphite ions was 0.224 mole/liter; the absoluteconcentration of acetate ions was 0.120 mole/liter; the temperature ofthe bath was approximately 99 C.; and the initial pH of the bath was inthe range 4.90 to 5.01. From Fig. 3, it will be observed that theminimum spontaneous decomposition, as determined by the drop in pH ofthe bath after three hours, occurred when the ratio was in the'range0.25 to 0.60. Of course, it will be appreciated that the pH drop of thebath is a direct function of the spontaneous decomposition thereof,since the uncontrolled chemical reduction oi the nickel cation willproduce the acid corresponding to the anion of the originally employednickel salt in amounts corresponding to its mass. In these tests, aswell as in the others herein referred to, the pl-I values weredetermined at room temperature.

It will be understood that the higher absolute hypophosphite ionconcentrations yield higher rates of deposition of the nickel withoutmaterially impairing the stability of the both within the optimumNi++/(H2POz) ratio. On the other hand, if the absolute concentration ofhypophosphite ions is increased substantially above the optimum range(0.15 mole/liter to 0.35 mole/liter), both the amount of nickel platingobtained during a given period and the quality of coating areconsiderably decreased by virtue of the random chemical reduction of thenickel ions that takes place and produces the black precipitate which,in turn, causes roughness and porosity in the coating, as previouslymentioned. This circumstance is illustrated by the curve 24 of Fig. 4which shows as abscissae theconcentration of the bath and, as ordinates,the weight of the plating deposited in periods of two hours, in

milligrams per square centimeter.

In these tests, the results of which are plotted in Fig. 4, the objectplated was formed of mild steel; the Ni++/(H2POz)- ratio was 0.330; theWA ratio was 100 cmfi/S cm.?; the temperature of the bath wasapproximately 99 0.; and the initial pH of the bath was approximately5.0. 'These tests showed a maximum plating deposit with a hypophosphiteconcentration of 0.224 and :this coating was bright and smooth with onlya ztrace of black precipitate but as the'concentraition increased theblack precipitate increased very rapidly and the plating became veryrough. As the hypophosphite ion concentration is decreased below thepreferred value, the black precipitate is only a trace and the platingis good but dull in appearance.

For purposes of comparison and to demonstrate the advantages of thediscoveries of the present invention, tests have been made using sodiumhypophosphite and an absolute concentration of hypophosphite ion equalto that specified by Brenner and Riddell for their bath No. 4 (and inthe same order of magnitudeas in'their other baths), viz., 0.095 molesper liter, in coating a mild steel sample with a fixed acetateconcentrationof .120 mole/liter, at a V/A ratio of 50 cm. /20 cm. =2.5,at an initial pH of about.

5.5 and at abath temperature of 99 C. for a period of thirty minutes,withthe results which are shown by curve 26 in Fig. 5, where theabscissae show the ratio of nickel ions to hypophosphite ions and theordinates show the weight of the plating deposited in milligrams persquare centimeter. With this low nickel hypophosphite ion concentration,it was found that when the ratio of nickel ions was very low (between.179 and .368) there was no plating deposit. The plating was at amaximum when the ion ratio was .368 and it gradually decreased as thisratio increased. The plating was good until'the ratio of 1.325 wasreached when it appeared slightly stained.

Using the same baths with sodium hypophosphite, these tests wererepeated at a V/A ratio of 2.5 and at a temperature of 99 C. with thehypophosphite ion concentration constant at .224 mole/liter and theresults are shown by the curve 28 in Fig. 5. Thus by substantiallydoubling the absolute hypophosphite ion concentration used by Brennerand Riddell, considerably higher rates of deposition can be obtained,while the stability of the baths is very little impaired at the optimumNi '/(H2PO2) ratio. When the ratio of nickel ions to hypophosphite ionswas in the range between 0.2 and 0.6, the nickel plating was good andvery bright.

With the same absolute concentration of hypophosphite ion (.224mole/liter) derived from sodium hypophosphite as in the testsrepresented by curve 20 in Fig. 5, and using a similar series of baths,but plating at a higher V/A ratio (50 cmfi/S cm?) :10, at a temperatureor about 99 C., the amount of nickel deposited in 60 minutes, with aninitial pH of 5.50, was as shown by the curve 30 in Fig. 6. At the lowerratios of nickel ions to hypophosphite ions the weight of the platingdeposit was substantially greater and it was brightest and smoothest inthe region represented by the peak of the curve.

On further tests, using again the same absolute concentration ofhypophosphite ion (.224 mole/liter) derived from sodium hypophosphiteand with the same baths, but plating at a still higher V/A ratio (100cm. /5 cm?) at about 99 C. the amount of nickel deposited in two hourswas as indicated by the curve 32 in Fig. 7. The deposit was dark andnonmetallio under the conditions represented by the beginning of thecurve but was good at all other times. A study of the curves shown inFigs. 2, 5, 6 and 7 shows a defi-' nite maximum weight of deposit whenthe ratio N1++/ (HzlI- O2)- is between 0.25 and 0.6.

So faras nickel efficiency is concerned, i. e.,

the weight of available nickel deposited includ-' ing thenickel-phosphorus compound), it decreases as the ratio Ni /(H2PO2)increases as is shown by the curve 34 in Fig. 8, using the same bath asthat employed for the experiments represented by the curve 25 in Fig. 5,and with a hypophosphite concentration of 0.095 mole/liter. The regionof optimum ratio (between 0.25 and 0.60) 7 proved vastly superiorto thatused by Brenner and Riddellf With an absolute hypophos-.

phite ion concentration} of .224 mole/liter the nickel efliciency atcompletion was 97.5% for a Ni++/'(H2PO2)2 ratio of .357 and 25.0% for aNi++/(II2POz)z ratio of 1.33 (B. & Rh). As previously indicated, a lowpH in the bath will increase the pressure of dissolution of thecatalyst(if the catalyst is acid soluble) and of the deposited nickel accordingto the Reaction 3 appearing above and will lower the reducing power ofthe hypophosphite; On the other-hand, a high pH tends to favor theformation and even? tual precipitation of basic nickel salt and topro-.-

iiibtie criisting"-atthe' caitaiytic -"'iirf 'a*ce. sh'dwhfibove, theoptimum 'platir'igre'sult' ith a simple bath containing nickel ions,hypoph'osphite ions and acetate ions 'p'an be obtained "15y usin ahypop'h'osphit'e ion concentration of around 0.2 mole/liter and a, IIit+/(H2PQ 2)L ratio of about 11-25 to 0560, Plating solutions wereprepared, according to these teachingsconteinihgolm II'lOl/Iilii orhypophosphiteionde- 1, rived from sodium hypophosphite-With variable Ni/(HZ'POZ) ratios and the usual 'bu'ffer con;- .cnt1a;ti0h (0.120mole/liter); The iriitia-l pH was adjusted by the 'additionofia'ceticacid. usi 'a medium V/A "ratid of 50 c'rn. 'volume 0115 *cmfjarea'ofcatalyst oromjthedeposits ofnickel T minutes at '99 C, were as shown bythe 'nickel deposited with .varying..ratios of nickel hypopiidsehite,"h'ave been "plotted "to "rori'n' the :gurves 42 and, respeotivelyshownin With the ratios o ni kei ionstogHypq hdspri te ions representedthe peaks thep'iafing wasfal'so.thehrightestafid In g neral, thelow'erjpH 'ir'aluje ap eared to 'gi 'e better is'filt'sbothasfto Hafiib'itfitdflth. plat-'- rng'deposit arid its tr'ieh. a g 3'fiie'iesults or test ilchlifaiiflielfi plotted to the Various 'curv'sShown in'F'i'gsJlto 10, inclusive, were made with sodium h'ypophosphite.For purposes of comparison, reference will now be made to testswh'ic theuse or 'eaicmm h'i' p'f firstito jthe efiectjo'fkzariat'io "j platingpath on the weight or ekefdepb ited a given period of. time when.plating 'with gal ic'iium hyp'o'phosphite aim "caljc'f' in a l tat e asa biifier, the results of tests are shown bi; thegcuryes 45, 48, iii)and EZshoWn-in Eigsi l liand lfi which record the eightfo'f thenickel-Ziepositeq in one ou "with IH/(m 0s) i-atios or .0268, 0.402,0:313 and-1.34.0, respectively. I H p J The vjariat'ion in the weightofthe nickel :de; posited with 'changeinjthia ratio .of then-icke l ionsto hypophosphitefions, yvithgclifierent pH Values, when. thehypophosphitelis pderivedj om calcium hypophosphite iii-the presence of.calcium faoetate as a buffer is shown hy tests',=-the"results of whichhavebeen'plottedtoiorm the cur-yes 54 and in Fig. 13, where theabscissae indicatethe ratios or nickel ions to higpophosphitQiOHSifindthe 'ordi'n'at'es show the ght in one hour in millig 7 Thehypoph'osphite 1 011 concentration .224 mole/liter,- the V/Aratio-was 50cm. /5 cm. and the acetate ion concentration was .120 mole/liter. Thecurve '5] shows the results when the pH of the-bath had a value of -eifland the curve 56 e als n tershows the results whenthepHewas increased to5.0. These results may be compared with those showmb y Fig. and alsowith those Fig. 7; which.represent-the-rsiilts of hypoph ph te ions deived fib 'rlfsodiiiiii *i'i'yiabphbsphit'e, r v

"absolutequaritity' rfbiiirr ntjin"thep1atifig bath;f

y t qhy r s nfi sa orm fiefqfai i f r 't 'eP h n on woii-1lthereiore"decrease' 'rapidly elow h li fe mjfl e at -i ns? i ib Q 1 m ntfi 1fksaf m w r nid w; eformdfduifi'ngtm plating 'operatio Q i i ma um mb nqf I dwh'ioh, in turn is afundtion F P'Q os'blfi flniav l-Thetheoretica' l needed bufier con'centrat n is "the ion of an organicacid eguivalent to two carbQXi L mu eriever ke i h t t-c ids sif xro treb e, m e fija f fl "oiie mate dfifickel. An excess of buffer other hand,is objectionablefs'ince it iwill the'formation ofba's" "h'ickel salts.efp ir 'hfie h f mii ive the best "results maybe efi tee ing- -calcu fiTo 'suniiiiai izefsjonie' of I the conclusionsj'which fm'ayf e tl'rawnfrom the foregoing disclosure, it I hes e that fijinjorder to obtainmgmetes bf gmke i'pl'at byri e fia' m n f qi l s iquebusc'idjgafth;without'excessive formatio or black Ipitate' uncontrolled, iandii ire;- =duot nofl nickel) the folldwing'coiiditions should z ulfi'd o of 'fii 'ckel ions to "hypoph osphfite io s in tn 31 1 should bebetween 0.25 nd "0160, depending 'uponj thespecific cation present. r

' 'IT e'co'ncentration of the bath in. hypqphos p M 319115 oi ldbe above0.15 mole/liter and vewww .7

3. The-pptimum-initiai pH v alues'of the bath 'u'nderQthe conditionsindicated in the two next preceding paragraphsare in the range betweenligand 5.5 5, Foriins tance, with sodium hypo phosphite, f 'there aretwo optimuminitial pH va u s; 0 4.f6 0 .and 5.50 while when Calciumhypogphosphite is employed the optimum initial pH hufi'er 'concentrationfin the bath should be equivalent to two ceirboxyl groups forev'e'ry nickel ion that can hedeposited. H V

5, The optimum ratio of solution volume of the bath topatalyt'icmaterial area (V/A) isbelow 1 0. I'tw i ll loe' understoodvthat theinvention is not limited except' as "defined by the appended claims.

WQLcIaim: I 1. The process or chemically plating with nickel a solidblody essentie 11y comprising anfeleinentselec'te'd from the groupconsisting Ofcopper, silver,"gold aluminum, iron, cobalt, nickel,palladium and platinum, which oomprises jc'ontaictingsaid. body with abath consisting essen} ti'ally of an aqueous "solution of a nickelsaltra'n'd a hypophosphite, wherein the ratio between nickel ions and flh pophosphite ions inesai'd bath expressed in insist concentrations isWithin the range 0.25 to 0.61 wherein the absolutejconcen trat ion ofhypophosphite ions in said bathe;- b i [l t 's., t t enew-1: t9 05%5,"andwhere the initial pH oi said bath is w hiii theap p r ximate range4.5 to 5.6. H f

The process set-'jforth in claim 1, wherein said hathconsistsessentially of an aqueous solution of a hickel salt stag hypophosphiteand buff effo'rmof e salt of an 'organic acid;

,a solid body essentially comprising an element selected from the groupconsisting of copper,

silver, gold, aluminum, iron, cobalt, nickel, palladium and platinum,which comprises contacting said body with a bath consisting essentially.of an aqueous solution of a nickel salt and a hypophosphite and abuffer in the form of an alkaline acetate, wherein the ratio betweennickel ions and hypophosphite ions in said bath expressed in molarconcentrations is within the range 0.25 to 0.60, wherein the absoluteconcentemperature of said bath is slightly below the boiling pointthereof.

5. The process of chemically plating with nickel a solid bodyessentially comprising an ele ment selected from the group consisting ofcopper, silver, gold, aluminum, iron, cobalt, nickel, palladium andplatinum, which comprises immersing said body in a bath consistingessentially of an aqueous solution of a nickel salt and a hypophosphite,wherein the ratio between nickel ions and hypophosphite ions in saidbath expressed in molar concentrations is within the range 0.25 to 0.60,wherein the absolute concentration of hypophosphite ions in said bathexpressed in mole/liter is within the range 0.15 to 0.35, wherein theinitial pH of said bath is within the approximate range 4.5 to 5.6, andwherein the ratio between the volume of said bath expressed in cm. andthe surface area of said body expressed in cm. is not greater than 10.

6. A bath for the chemical plating of a catalytic material with nickelconsisting essentially of an aqueous solution of a nickel salt and ahypophosphite, the ratio between nickel ions and hypophosphite ions insaid bath expressed in molar concentrations being within the range 0.25to 0.60, the absolute concentration of hypophosphite ions in said bathexpressed in mole/liter being within the range 0.15 to 0.35, and theinitial pH of said bath being in the approximate range 4.5 to 5.6.

'7. A bath for the chemical plating of a catalytic material with nickelconsisting essentially of an aqueous solution of a nickel salt and analkaline hypophosphite and a buffer in the form of a salt of an organicacid, the ratio between nickel ions and hypophosphite ions in said bathexpressed in molar concentrations being within the range 0.25 to 0.60.the absolute concentration of hypophosphite ions in said bath expressedin mole/liter being within the range 0.15 to 0.35, the absoluteconcentration of said buffer in said bath being approximately twocarboxyl groups for every nickel ion that can be deposited, and theinitial pH of said bath being in the approximate range 4.5 to 5.6.

8. A bath for the chemical plating of a catalytic material with nickelconsisting essentially of an aqueous solution of a nickel salt and analkali hypophosphite and a buffer in the form of a salt of an organicacid, the ratio between nickel ions and hypophosphite ions in said bathexpressed in molar concentrations being within the range 0.25 to 0.60,the absolute concentration of hypophosphite ions in said bath expressedin mole/liter being within the range 0.15 to 0.35, the absoluteconcentration of said buffer in said bath being approximately twocarboxyl groups for every nickel ion that can be deposited, and theinitial pH of said bath being in the approximate range 4.5 to 5.6.

9. A bath for the chemical plating of a catalytic material with nickelconsisting essentially of an aqueous solution of a nickel salt and analkali earth hypophosphite and a loufier in the form of a salt of anorganic acid, the ratio between nickel ions and hypophosphite ions insaid bath expressed in molar concentrations being within the range 0.25to 0.60, the absolute concentration of hypophosphite ions in said bathexpressed in mole/ liter being within the range 0.15 to 0.35, theabsolute concentration of said buffer in said bath being approximatelytwo carboxyl groups for every nickel ion that can be deposited, and theinitial pH of said bath being in the approximate range 4.5 to 5.6.

10.v The process of chemically plating with nickel a solid bodyessentially comprising an element selected from the group consisting ofcopper, silver, gold, aluminum, iron, cobalt, nickel, palladium andplatinum, which comprises contacting said body with a bath consistingessentially or an aqueous solution of a nickel salt and a hypophosphite,wherein the ratio between nickel ions and hypophosphite ions in saidbath expressed in molar concentrations is within the range 0.25 to 0.60,wherein the absolute concentration of hypophosphite ions in said bathexpressed in mole/liter is within the range 0.15 to 0.35, andmaintaining the pH of said bath within the approximate range 4.5 to 5.6.

11. The process of chemically plating with nickel a solid bodyessentially comprising an element selected from the group consisting ofcopper, silver, gold, aluminum, iron, cobalt, nickel, palladium andplatinum, which comprises contacting said body with a bath consistingessen-- tially of an aqueous solution of a nickel salt and ahypophosphite, wherein the ratio between nickel ions and hypophosphiteions in said bath expressed in molar concentrations is within the range0.25 to 0.60, wherein the absolute concentration of hypophosphite ionsin said bath expressed in mole/liter is within the range 0.15 to 0.35,and periodically correcting the pH of said bath by the addition theretoor a soluble alkali to maintain a value within the approximate range 4.5to 5.6.

12. The process of chemically plating with nickel a solid bodyessentially comprising an element selected from the group consisting ofcopper, silver, gold, aluminum, iron, cobalt, nickel, palladium andplatinum, which comprises contacting said body with an aqueous bathconsisting essentially of nickel ions, alkaline ions, hypophosphite ionsand acetate ions, wherein the ratio between nickel ions andhypophosphite ions in said bath expressed in molar concentrations iswithin the range 0.25 to 0.60, wherein the absolute concentrations ofhypophosphite ions and acetate ions in said bath expressed in mole/literare respectively approximately 0.225 and 0.120, and wherein the initialpH of said bath is in the approximate range 4.5 to 5.6.

GREGOIRE GUTZEIT. ABRAHAM KRIEG.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,207,218 Roux Dec. 5, 1916 2,430,581 Pessel Nov. 11, 19472,532,283 Brenner V Dec. 5, 1950

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A SOLID BODYESSENTIALLY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OFCOPPER, SILVER, GOLD, ALUMINUM, IRON, COBALT, NICKEL, PALLADIUM ANDPLATINUM, WHICH COMPRISES CONTACTING SAID BODY WITH A BATH CONSISTINGESSENTIALLY OF AN AQUEOUS SOLTUION OF A NICKEL SALT AND A HYPOPHOSPHITE,WHEREIN THE RATIO BETWEEN NICKEL IONS AND HYPOPHOSPHITE IONS IN SAIDBATH EXPRESSED IN MOLAR CONCENTRATIONS IN WITHIN THE RANGE 0.25 TO 0.60,WHEREIN THE ABSOLUTE CONCENTRATION OF HYPOPHOSPHITE IONS IN SAID BATHEXPRESSED IN MOLE/LITER IS WITHIN THE RANGE 0.15 TO 0.35, AND WHEREINTHE INITIAL PH OF SAID BATH IS WITHIN THE APPROXIMATE RANGE 4.5 TO 5.6.